In a case where a glass substrate is processed at a high temperature in, e.g., a CVD apparatus, the glass substrate may be broken due to heat or the like. In loading and unloading the glass substrate, the glass substrate is lifted up in a chamber while edges thereof are being supported and a pick of a transfer device is extended under the bottom of the glass substrate that has been lifted up. If the glass substrate is broken, only one part of the glass substrate is lifted up, so that a broken part of the glass substrate interferes with a moving path of the pick. Accordingly, the tip of the pick collides with the glass substrate, and the broken glass substrate is broken into pieces and the pieces are scattered in the chamber. It takes a lot of time to remove the broken glass substrate or pieces from the chamber and restore the apparatus. Further, an operation of a fabrication line is stopped until the apparatus is restored.
Accordingly, for example, Japanese Patent Application Publication No. 2003-60004 discloses a sensor for detecting a contact with an obstacle that is attached to a tip of a pick (robot hand).
In Japanese Patent Application Publication No. 2003-60004, sealed hollow members filled with a fluid, which are freely expanded and contracted, are attached to tips of picks. When the hollow members come into contact with an obstacle, the hollow members are deformed, and the pressure of the fluid sealed in the hollow members increases. The pressure increase is detected by a pressure sensor, thereby detecting that the tips of the picks come into contact with the obstacle.
Japanese Patent Application Publication No. 2003-60004 discloses a method in which an increase in the pressure of the fluid sealed in the hollow members is detected by a pressure sensor. Accordingly, in a case where a transfer device transfers a glass substrate in a depressurized environment, the hollow members are hardly deformed and it is difficult to detect the contact with an obstacle.